1. Field of the Invention
The present invention relates to a process for the polymerization of .alpha.-olefins and especially to the deactivation of the coordination catalyst used in a solution process for the polymerization of .alpha.-olefins. In particular the present invention relates to such deactivation wherein the coordination catalyst contains vanadium.
2. Description of the Prior Art
Polymers of ethylene, for example, homopolymers of ethylene and copolymers of ethylene and higher .alpha.-olefins, are used in large volumes for a wide variety of end uses, for example, in the form of film, fibres, moulded or thermoformed articles, pipe, coatings and the like.
Processes for the preparation of homopolymers of ethylene and copolymers of ethylene and higher .alpha.-olefins are known. Such processes include processes in which the monomers are polymerized in the presence of a coordination catalyst, for example, a catalyst comprising a compound of a transition metal belonging to Groups IVB-VIB of the Periodic Table and an organometallic compound of a metal belonging to Groups I-IIIA of the Periodic Table.
A particularly preferred process for the polymerization of .alpha.-olefins is the high temperature or "solution" polymerization process, an example of which is described in Canadian Pat. No. 660 869 of A. W. Anderson, E. L. Fallwell and J. M. Bruce, which issued Apr. 9, 1963. In a solution process the process parameters are selected in such a way that both the monomer and polymer are soluble in the reaction medium. Under such conditions accurate control over the degree of polymerization, and hence the molecular weight of the polymer obtained, may be achieved, for example, by control of the reaction temperature.
The polymerization reaction in a solution polymerization process is normally terminated by addition of a so-called "deactivator", for example, a fatty acid or an alcohol. The fatty acid is admixed with hydrocarbon solvent, normally the solvent of the polymerization process, and fed into the polymerization mixture, usually shortly after that mixture passes from the reactor. The polymerization mixture that has been treated with deactivator contains catalyst residues which may be removed by contacting the mixture with an adsorbent, for example, alumina. Such a deactivation and catalyst removal process is described in Canadian Pat. No. 732 279 of B. B. Baker, K. M. Brauner and A. N. Oemler, which issued Apr. 12, 1966.
A method for the deactivation of a coordination catalyst in a high pressure solvent-free process for the polymerization of .alpha.-olefins is disclosed in U.S. Pat. No. 4,105,609 of J-P. Machon, B. Levresse and P. Gloriod, issued Aug. 8, 1978. The method involves injecting into the polymerization reaction mixture an alkali or alkaline earth metal salt of a carboxylic acid e.g. sodium stearate, calcium stearate or sodium benzoate.
The stabilization of polyethylene by the addition of up to 5% by weight of a polyvinyl chloride stabilizer is disclosed by I. O. Salyer et al in U.S. Pat. No. 2,985,617, which issued May 23, 1961. The disclosed stabilizers include alkaline earth salts of fatty acids.